In material processing by means of laser radiation, laser beam scanning of the zones to be processed on the object is generally employed. The precision of positioning the laser beam usually determines the precision achieved in said processing. Focussing of the laser beam into a processing volume requires exact three-dimensional positioning. Therefore, for high-precision processing it is usually indispensable to hold the object in an exactly defined position relative to the laser processing device. The above-mentioned adapter is intended for such applications because it fixates the object to be processed or imparts a desired shape to the deformable surface of the object to be processed.
This is required, in particular, for micro-processing of materials which have only a low linear optical absorption in the spectral range of the processing laser radiation. For such materials, usually non-linear interactions between the laser radiation and the material are employed, in most cases in the form of an optical breakthrough generated in the focus of the laser beam. Since the processing action takes place only in the laser beam focus, exact three-dimensional positioning of the focal point is indispensable. Thus, an exact depth position of the focus position is required in addition to a two-dimensional deflection of the laser beam. The above-mentioned adapter facilitates this because it ensures constant optical conditions, which are also known with a certain precision, in the beam path to the object, or because known optical conditions, in particular refractive conditions, are present in the beam path when the adapter contacts the object.
A typical application for such an adapter is the ophthalmic surgery procedure known as LASIK, wherein a laser beam is focussed into the cornea on a focal point which is of the order of magnitude of one micrometer. A plasma then forms in the focus, which plasma causes local separation of the corneal tissue. By suitable serial arrangement of the local separation zones generated in this manner, macroscopic cuts are realized and a certain partial volume of the cornea is isolated. A desired change in refraction is then achieved by removal of said partial volume, so that correction of a visual defect is possible.
Exact positioning of the laser beam is indispensable to carry out the method. For this purpose, a contact lens provided with reference marks is known from U.S. Pat. No. 6,373,571, said lens realizing an adapter of the aforementioned type. This contact lens is adjusted by means of a separate measurement device, which results in a relatively complex structure. The aforementioned adapter serves two functions: not only does it ensure the required optical properties for the laser beam to enter the cornea, but it also fixates the eye, preferably with respect to several degrees of freedom, particularly preferably with respect to all possible degrees of freedom. This prevents movements of the eye relative to the laser processing device.
An example of such adapter is described, for example, in WO 03/002008 A1. The adapter referred to therein as “applanation lens” comprises a suction ring, which is attached to the eye by means of suction. Inserted in the suction ring is a glass plate, which is pressed into the suction ring by means of a bracket. The bracket simultaneously also fixes a flange part to the suction ring, which flange part is permanently attached to the laser processing device. The multi-component adapter of WO 03/002008 A1 presses the surface of the cornea flat, thus achieving simple standard geometries. However, this is very inconvenient for the patient. Moreover, applanation of the corneal surface is undesired in some surgical operations.
A further example of an adapter of the aforementioned type is described in EP 1,159,986 A2. It has reticle markings at the edge of a holder, which make visual alignment possible for the surgeon. However, the precision achieved thereby is not always sufficient.
Therefore, it is an object of the invention to improve an adapter or a laser processing device of the aforementioned type such that high-precision laser processing is easily possible.